This invention relates generally to manufacturing processes and devices used therein for the manufacture of magnetic recording media to be used in making flexible, magnetic recording disks. Specifically, this invention relates to a manufacturing process and device for providing magnetic media in which the particles are essentially unoriented.
During the production of flexible, magnetic recording media, when the magnetic particles become aligned in some particular direction (the medium becomes anisotropic), the magnetic and the recording properties are different in different directions. A preferential particle direction along the web will provide a disk with an output signal higher at that direction than along other directions and, consequently, the level of a recorded signal read from the disk will change as the disk or head rotates.
In certain uses of flexible media (such as in the manufacture of recording disks), this linear orientation is not desired. Such particle orientation with said anisotropic properties produces a modulation of the read-back signal amplitude because the azimuthal angle between the average direction of the particles and the gap of the read/write head changes along any circular path concentric with the center of the disk. It can be advantageous to have a highly linearly-oriented product when the product is to be used as a linear magnetic recording media (e.g., tape), but it is disadvantageous to have linearly-oriented products whose final end use is in the manufacture of a flexible, magnetic recording disk stamped from a coated web.
Prior to the present invention and at the present time, when a coating is needed in which the magnetic particles are not to be linearly oriented (e.g., in a flexible, magnetic recording disk), a semi-disoriented medium is obtained by physically removing the orienting magnet from the manufacturing process. Even without the use of an orienting magnet, however, the process of casting linear magnetic recording tape will still produce a certain amount of linear orientation.